Quadrature voltage controlled oscillator plays an important role in modern wireless communication systems, and it is particularly useful in applications that require high fidelity quadrature signals, such as in wireless and wired transceivers. One of the most popular type of quadrature voltage controlled oscillator is LC quadrature voltage controlled oscillator, and it comprises two symmetric LC tanks voltage controlled oscillators coupled with each other. Typically, LC quadrature voltage controlled oscillator can be classified into parallel-coupled quadrature voltage controlled oscillator (P-QVCO) and series-coupled quadrature voltage controlled oscillator (S-QVCO). For P-QVCO, the For P-QVCO, the coupling transistors are arranged in parallel with the switching pairs, whereas for S-QVCO, the transistors are stacked for series coupling.
In general, P-QVCO and S-QVCO can provide good phase noise performance and have relative low power consumption. However, they suffer from various problems. For example, the coupling transistors in both P-QVCO and S-QVCO may introduce additional noise, and as a result the phase noise of the quadrature voltage controlled oscillator may be degraded. Also, the oscillation efficiency in conventional P-QVCO and S-QVCO is generally low.
Accordingly, there exists a need to provide a quadrature voltage controlled oscillator that is more efficient in operation, compact in design, and more importantly, less prone to the above problems.